One-step microwave-assisted synthesis of photoswitchable hybrid organic-inorganic nanostructures based on styrylquinoline ligands and CdS quantum dots. Chaschikhin O.V., Budyka M.F. 1 Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Russia E-mail:ovchash@icp.ac.ru, ovchasch@gmail.com
In the past few years organic-inorganic hybrid nanostructures (HS) have been actively investigated. HS is an inorganic nanoparticle (such as quantum dot, Qd) modified by organic ligand (L). For modification of CdS Qd’s are widely used organic molecules with thiol group, which attaches L to the Qd’s surface [1, 2]. We have developed novel one-step microwave-assisted synthesis (without ligand exchange and surface modification of Qd, adding photoactive L at the stage of Qd’s synthesis) of HS, based on photoactive styrylquinoline ligands (2-(E)-(4-[9-mercaptononoxy]styryl)quinoline as L1 and N-methyl-2-(E)-(4-[9-mercaptononoxy]styryl)quinoline iodide as L2) and semiconductor CdS Qd’s (diameter 2.4 nm). Spectral properties of HS are superposition of component’s (Qd and L) spectral properties. Irradiation of L1 as in “free” form, so as in HS Qd-L1 leads to it’s trans-cis photoisomerization, what allows to switch spectral and luminescent of whole HS. In HS Qd-L2 quenching of Qd’s luminescence by L2 is observed, but irradiation of system with light leads to destruction of system (L2 and Qd both), presumedly due to electron transfer process, whar does not allow to switch luminescence of the system. Composition of hybtid structures
Synthesis of HS Qd-L
For the synthesis of HS’s we used an experimental setup based on a magnetron Daewoo 2M218 HF with a power of 920 W equipped with a cylindrical working chamber of 125 mm in length and 100 mm in diameter. A solution of 13.3 mg (0.05 mmol) cadmium acetate dihydrate (SigmaAldrich, >98%) and L in 2.5 mL DMF (chemically pure) was supplied with 0.5 mmol benzyl mercaptan (SigmaAldrich, 99%), after that, 2.5 mL of a DMF solution containing 3.8 mg (0.05 mmol) thiourea (reagent grade) was added. Ratio of reagent’s concentration is final solution was C(Cd2+):C(thiourea):C(L) = x (see in table). The resulting reaction mixture was subjected to microwave irradiation for 40 s. A 1 mL aliquot of the solution was collected in a test tube; it was supplied with 4 mL ethanol and centrifuged for 1 hour in a OPn-3.02 Dastan centrifuge at the rotation speed of 3000 rpm; the supernatant was then decanted. Five milliliters of ethanol was added to the sediment remaining on the bottom of the tubes. After that, the centrifugation was repeated, the solution was decanted, and the resulting precipitate was dried under vacuum. As a result, powders of pale yellow colors were obtained. The resulting samples (see table) were dissolved in DMF; their absorption and luminescence spectra were studied.
Hybrid structure consists of 2 chromophores, i.e. its composition may be found by spectrophotometrical analysis treating it as 2component system. Quantity of L, attached to Qd (see table) is counted by ratio of Qd and L absotption bands. This quantity fot HS’s Qd-L1 may be approximated with exponentional function (fig.5).
Spectral properties of Qd, L and HS’s 2
1
14
1.0
I, a.u.
7
x
n(L):QD
Qd-L1-1
0.05
1
Qd-L1-2
0.1
1.3
Qd-L1-3
0.2
3.5
Qd-L1-4
0.25
5.5
Qd-L1-5
0.3
12.7
Qd-L2
0.3
5
n(L1) in HS Qd-L1
4 12
0.8
6
HS
5
5
3
10
0.6
A
5
4
8
0.4
4
6 0.2
3
1
1
2
4
0 300
350
400
450
300
350
400
450
500
550
600
, nm Fig. 2. Luminescence spectrum, 1nm– HS QD-L1-2 Fig. 1. Absorbance spectrum of Qd (1), L1 (excitation on 330 nm), 2 –- L (excitation on 360 nm), (2), HS Qd-L1-1 – QD-L1-5 (3-7). 3 – Qd (excitation on 330 nm) and excitation spectrum 4 –- HS QD-L1-2 (observation on 500 nm), 5 – HS QD-L1-2 (observation on 400 nm ).
2
0 0.05
0.10
0.15
0.20
0.25
0.30
x Fig. 5. Number of L1 in HS’s Qd-L1 as function of x
1.0
1.0
0.8
2
1
3
4
0.8
Research was supported by the Russian Foundation for Basic Research, project
A 0.6
0.6
13-03-00636.
0.4
References. [1] J. Claussen, N. Hildebrandt, K. Susumu, M. Ancona, I. Medintz // ACS Appl. Mater. Interfaces, 2014, 6, 3771–3778 [2] W. Algar, H. Kim, I.Medintz, N. Hildebrandt // Coordination Chemistry Reviews, 2014, 263– 264, 65– 85
1
A
3
2
0.4
0.2
0.2
0.0 300
, nm
400
500
Fig. 3. Absorbance spectrum of Qd (1), L2 (2), HS Qd-L2
400
450
500
550
600
, nm Fig. 4. Luminescence spectrum 1 – HS QD-L2 (excitation on 330 nm), 2 –- L (excitation on 420 nm), 3 – Qd-L2 (excitation on 420 nm), 4 – Qd-L2 (excitation on 330 nm)
Spectral properties of HS are superposition of Qd and L spectral properties (fig. 1-4). In HS Qd-L2 quenching of Qd’s luminescence up to 40 % was observed.